Short answers, pulled from the story.
Oleg the Wise was a Varangian prince who became the first prince of Kiev and laid the foundations of Kievan Rus', the medieval state that preceded modern Russia, Ukraine, and Belarus. He seized Kiev in 881-882 by killing its rulers Askold and Dir, and consolidated control over East Slavic tribes along the Dnieper river.
The Primary Chronicle dates Oleg's death to 912, while the Novgorod First Chronicle gives 922. The Schechter Letter, a Jewish Khazar document, describes a Rus' warlord named Helgu who was active as late as the 940s, leading some scholars to question the traditional date entirely.
Pagan priests prophesied that Oleg would die because of his stallion. He sent the horse away to escape the prophecy, but years later visited the horse's bones and touched the skull with his boot. A snake emerged and bit him, killing him and fulfilling the prophecy. Alexander Pushkin retold this legend in his ballad "The Song of the Wise Oleg."
The Schechter Letter is a document written by a Jewish Khazar contemporary of Byzantine Emperor Romanus I Lecapenus. It describes a Rus' warlord named HLGW (transcribed as Helgu), placed in the 940s. Scholars including David Christian and Constantine Zuckerman have argued it refers to Oleg or a figure in his political tradition, challenging the 912 death date.
The Primary Chronicle claims a Rus' victory in the 907 campaign against Constantinople, but historian Vladimir Shikanov argues the Rus' were defeated at Cape Tricephalus by Byzantine fire-fighting ships under Patrikios John Rodin, and that the chronicle account was a later rewrite. The subsequent treaty of 911 is a documented historical fact, though historians disagree on its terms.
Prince Oleg appears as the primary villain in season 6 of the television series Vikings (2019-2020), played by Russian actor Danila Kozlovsky. In that production, Askold and Dir are portrayed as his brothers, a departure from the chronicle accounts.